Locals and rescue workers clear the rubbles of a partially collapsed overpass in Kolkata, Thursday, March 31, 2016. Rescuers dug through large chunks of debris from an overpass that collapsed while under construction Thursday, killing many people and injuring scores of others, officials said. (Swapan Mahapatra/Press Trust of India via AP) INDIA OUT, CREDIT MANDATORY

KOLKATA, India (AP) — A long section of an overpass under construction collapsed Thursday in a crowded Kolkata neighborhood and sent tons of concrete and steel slamming onto midday traffic, killing at least 21 people and leaving scores of others injured, police said.

More people were feared trapped in the debris, and rescuers used saws, small cranes and their bare hands to search for survivors. Smashed yellow taxis, destroyed rickshaws and the bloody legs of trapped people jutted from the fallen girders and concrete.

The overpass spanned nearly the width of the street and was designed to ease traffic through the densely crowded Bara Bazaar neighborhood. About 100 meters (300 feet) of the overpass fell, while other sections remained standing.

It “came down with a huge crashing sound,” said Yogesh Sharma, who was sitting at a roadside tea stand with friends.

“I left my cup of tea and ran,” said Sharma, a 23-year-old resident. “I was crying at the spot.”

At least 21 people were killed, a police official said on condition of anonymity because he was not authorized to speak to the media. More than 70 people were taken to two hospitals in Kolkata, the state capital, officials said. It was not immediately clear how many people were missing.

Army troops and personnel from the National Disaster Response Force joined the effort to pull people from smashed vehicles. Huge cranes and other equipment were brought to the site to begin clearing the rubble. Workers also used cutting torches to pry open the slabs.

The operation was a “very, very challenging task,” said O.P. Singh, chief of the disaster response force. Rescuers also used dogs and special cameras to find people who were trapped, he said.

“The area was very, very crowded. Motorized rickshaws, taxis … there was a lot of traffic,” one witness told NDTV television.

Mamta Banerjee, the top elected official of West Bengal state, said a private builder had missed several deadlines for completing the construction.

The contract for the overpass was signed in 2007 and it was expected to be completed in two years. Banerjee accused the previous Communist government in West Bengal of not adhering to building regulations.

“We completed nearly 70 percent of the construction work without any mishap,” said K.P Rao, a top official of IVRCL Infrastructure company, which was building the overpass. “We have to go into the details to find out whether the collapse was due to any technical or quality issue.”

“It was a total act of God,” said his colleague, Dilip, who uses one name.

Building collapses are common in India, where regulations are poorly enforced and construction companies often use substandard materials.